Various liquid dispensing systems have been developed for the precise application of a heated liquid onto a substrate. Dispensing systems for supplying liquid material in the form of filaments or other patterns are known in the art. These dispensing systems are conventionally used to apply thermoplastic materials, such as a hot melt adhesive, to various substrate materials during the manufacturing of diapers, sanitary napkins, surgical drapes, and other products. Typically, liquid material and pressurized process air are supplied to the dispensers where they are heated and distributed to one or more dispensing modules for application to the substrate. The heated liquid material is discharged from the dispensing module while pressurized process air is directed toward the dispensed liquid to attenuate or draw down the dispensed liquid material and to control the pattern of the liquid material as it is applied to the substrate.
Conventional liquid dispensing systems typically utilize a manifold for heating and distributing the pressurized process air and liquid material to the dispensing modules. The manifold generally has a block configuration having a pair of opposed front and rear surfaces, a pair of opposed end surfaces, and opposed upper and lower surfaces. The manifold is configured to accommodate a number of dispensing modules that releasably couple to the manifold. The dispensing modules may, for example, span the front surface. In any event, for each dispensing module coupled to the manifold, the manifold has a liquid passage ending in a liquid outlet for feeding heated liquid to the dispensing module and a process air passage ending in a process air outlet for feeding heated process air to the dispensing module. The dispensing module includes a liquid inlet and a process air inlet that communicate with the liquid outlet and process air outlet in the manifold. The dispensing module further includes a pneumatically or electrically actuated valve assembly for metering a precise quantity of the liquid and discharging the metered amount through a small-diameter dispensing orifice and onto a typically moving substrate positioned below the orifice.
During maintenance of the liquid dispensing system, such as when the dispensing modules become clogged with debris or a different dispensing module is to be used for a specific application, a dispensing module will be removed from the manifold. During the maintenance of the liquid dispensing system the system is not hydraulically pressurized, however, residual or hydrostatic pressure often causes a small amount of liquid to drip from the liquid outlets of the manifold and down the front surface. Because the dispensing modules are generally vertically oriented, the liquid outlet is positioned vertically above the process air outlet in the manifold. Thus, liquid that drips from the liquid outlet flows down the front surface of the manifold and may enter and pool in the process air outlet and adjacent passage.
In the normal course, a new or repaired dispensing module is simply reattached to the manifold and the system is powered back up for production without removing the liquid from the process air outlet. Attempts may be made to remove the liquid (which may have solidified) from the process air outlet and adjacent passage, but frequently fail due to the difficulty in removing enough of this liquid. Liquid in the process air passage and outlet may result in a blocked process air outlet. This prevents the desired pattern from being formed on the substrate resulting in scrap product. Moreover, liquid in the process air outlet may cause the process air passageways in the dispensing module to become clogged. In any event, the liquid dispensing system must be shut down to repair or replace the damaged dispensing modules, thereby increasing system downtime and increasing overall production costs.
A need therefore exists for an improved liquid material dispensing system which overcomes various drawbacks of prior dispensing systems, such as those described above.